So, I understand the sentiment behind the idea that those who are already getting tons of money for their tv show/movie shouldn't be further charging fans for autographs, BUT I think people often underestimate how quickly the money that these guys make is used up.
From briefly googling scooby salaries, it seems that, for example, Nick Brendon made somewhere between 8-10 million for the entire run of Buffy. Let's say he made 10. Something close to half that goes to taxes in the US, at that income bracket. So right away, he's down to 5 mil. I would think that about 1 mil of that goes to his agent, so now he's down to 4, (keep in mind, this is in 2003). Presumably he lives in LA so that he can continue to take auditions and smaller gigs as they come along. It costs a lot to live there--I mean sure he can be smart about it but it's not like he can move to a place in the country where it would be much easier to save his money, instead.
So then, even while he's not generating any income, he has to pay his agent and (possible) manager, so that he can keep getting gigs and public appearances.
So by 2012, how much of that 4 million that he was left with in 2003 from the show does he realistically have? Not enough to live off for the rest of his life, especially if he has a family to support, (which I guess he doesn't, yet).
Someone like James Marsters whom I believe supports 2 kids and made around the same amount, (possibly more?), definitely has to do everything he can to milk his former persona. It's reeeaaally tough out there to land things, especially once you hit 50, no matter how incredibly talented you are.
My family member was on arguably the most famous TV show as a recurring character, and has struggled to work regularly since, in spite of the fact that he's fiercely talented and works his butt off. People know him as his former character, and he has to use that to his advantage as much as possible, on the other side of the camera.